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Can a contra-rotating helicopter simply tilt its entire rotor set instead of using a cyclic?
I was reading this interesting question and, per answer #1, a normal helicopter cannot do it because gyro effects would probably mean the body of the helicopter would tilt more than the rotor.
So now I think about contra-rotating helicopters, like the Kamov Ka-50. They don't need tail rotors, because the contra-spin cancels out reaction torque (except when they want to yaw, for which they extend little things at the blade tips of one rotor, producing more torque there and therefore opposite yaw).
Anyway, can't a contra-rotator just tilt its whole hub instead of using traditional cyclic (swash plate, scissors link, which in fact are a lot more complex for a contra-rotating helicopter).

I'm guessing the forces required to tilt the huge gyroscope (rotor) is going to be the biggest issue.

@RonBeyer But contra-rotating blades cancel out gyro forces as I said in 2nd paragraph.

It doesn't cancel out the gyro forces, it cancels the torque (as you said) that would cause the helo to yaw. The gyro forces are still there.

@RonBeyer Why would it not also cancel out the gyro forces? See Peter Kampf's answer to this question: http://aviation.stackexchange.com/questions/31614/do-gyroscopic-forces-from-rotating-engines-significantly-affect-yaw-or-pitch

It won't cancel the angular momentum, which is what Ron is referring to. What will be cancelled is the tendency for a pitch change to cause a roll or vice versa. With contra rotating blades a roll to the right will cause one rotor disc to try to pitch up and the other to pitch down. That's the effect Peter is talking about. Tying to use the weight of the helicopter to overcome the angular momentum is not going to give you much result. They would turn each other. But changing the lift from one part of the disc to the other is  using the aerodynamic forces to overcome the angular momentum.

@KorvinStarmast Tilt. Edited. By tilt, I mean rotate the axis that the blades rotate around.

Please do not use references like "answer #1" because the order of the answers is not immutable

Juan de la Cierva, inventor of the autogyro, on the C.30 went to a tilting rotor. Most autogyros tilt the entire rotor for cyclic control. Some autogyros apply engine torque to the main rotor to assist in achieving short takeoffs. Now for this brief time, the autogyro is functioning like a helicopter, and the main rotor is driven by the engine prior to takeoff. There is now a torque from the engine acting on the airframe, that requires more pilot hand force to control the rotor while the engine is driving the rotor. Counter-rotating rotors on a helicopter would neutralize the reaction torque into the airframe. So yes for a very small helicopter, it should be possible to tilt the main rotor for cyclic control, without hydraulic power assist. If one is going to use a swashplate for collective control, it is easier to just control cyclic conventionally.
Here is one example of a helicopter that tilted the rotor for the cyclic:
http://www.aviastar.org/helicopters_eng/bensen_zipster.php

I don't understand your idea of "tilting the shaft", how would you do that? With the cyclic control it is very easy to tile the aerodynamic force but not the whole helicopter, why would you use a more complex mechanism of tilting the shaft (and the engine), and how would you do it? The gyroscopic effect will work against you and I have in mind no way to move a so big part of the Mass of the helicopter.
Moreover, since you are referring to another question that already has an answer, do you think it is easier to tilt a single shaft or the double coaxial shaft of the Ka-50?
The cyclic system gives a direct response to input and it is a very simple system. To prove it, try to Google AW609, that is a convertiplane working with the principle you talk about. See how complex, risky and expensive a convertiplane is and you will realise it in few seconds!
The V-22 Osprey (Like the AW609) tilts the whole engine, and it is a hell of a system, very complex, expensive, risky and not competitive. The advantage there is to have something that can be VTOL but can flight faster than an helicopter. A pure helicopter that tilts the rotor would have no advantage and only disadvantages!

Tilting the shaft, the way I imagined it, would be tilting the entire hub. The engine is part of the hub. Power for the tilt would be supplied from the engine. Some part in the hub pushes against the hull, rather than a part from the hull pushing against the hub. They are really the same thing. As for exactly how, idk but they already do it on the tiltrotor V-22 Osprey. BTW this heli would not have much more total weight than a normal heli, which still has an engine somewhere, just in a different place.

@DrZ214 the V-22 Osprey (Like the AW609) tilts the whole engine, and it is a hell of a system, very complex, expensive, risky and not competitive. The advantage there is to have something that can be VTOL but can flight faster than an helicopter. A pure helicopter that tilts the rotor would have no advantage and only disadvantages!

The cyclic does not "tilt" the disc.  It cyclically alters the blade pitch to vary the angle of attack which causes an increase or decrease in the lift produced cyclically around the blade orbit. The blade "flies" into position with the blade reaching a maximum where the swashplate is at it's maximum and a minimum 180 degrees later.  For complete accuracy, due to precession, the cyclic input is made 90 degrees in advance of the desired lift change.
The disc is titled by aerodynamic forces and therefore from the power input from the engine.  It is not moved by the forces applied by the cyclic control and links.
The cyclic on a light helicopter is generally connected directly to the swashplate with mechanical links.  The disc tilt can be controlled with the lightest of touches. In a hover in no wind, you can move by applying pressure to the cyclic with the cyclic barely moving.  A tiny force on the swashplate results in a large force on the disc.
If you used links to mechanically move the entire disc, rather than causing the large aerodynamic changes, it would have to oppose them.

It's the twin-rotor that can't do it!
To control the attitude you have to create a torque. You do that by offsetting the aerodynamic force (lift) from the centre of mass, and whether you do it by changing the lift distribution or shifting the centre of mass does not matter too much. Except you can achieve larger change by changing the lift distribution (via cyclic control).
Now however helicopter rotor is a gyroscope and that does complicate things quite a bit. The gyroscopic effect means that applying sideways torque makes the craft pitch and forward and aft torque makes it bank—the force must be applied 90° ahead of the direction you want to bank in the direction of the rotor rotation.
For cyclic, the links actually ride the swashplate ahead of the blades, so when you tilt the swashplate forward, the advancing blade pitches down, which makes it start to descend and reach the lowest point in front and everything pitches down nicely.
But when using weight-shift to get the same effect, with counter-clockwise-rotating rotor you'd tilt the rotor right (shift weight right, effectively). It would be rather weird, but with the controls properly rigged probably possible.
However on twin rotor, shifting weight to the right will make one rotor want to pitch forward, but the other one want to pitch aft. And they'll just twist and stress the shaft, but not do anything! The cyclic easily solves this, because is decreases the lift at different place on each rotor so they both want to tilt the same way, but weight shift can't do that.
So you could do it on a single-rotor craft. It would not really be simpler (tilting driven, spinning axles is not easy) and allow less manoeuvrability, but it would work. With counter-rotating rotors you can tilt each differently to get the desired effect (the tiltrotors do that). But with contra-rotating rotors you can't tilt each differently as they are on the same axis, so you can't do it this way at all and cyclic with a swash-plates and scissor-links is the only option.


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Can fighter jets be reloaded with ammunition mid-flight?
I know that we can re-fuel fighter jets mid-flight, but do we have also a mechanism to reload them with ammunition during mid-flight so they don't need to go back to base to reload?

The rearming aircraft, along with all of its armament, would be a HUGE target both physically and strategically. The risk is much greater than the reward.

Short answer: no.
Longer answer: you would need to design a carrier craft that could store large quantities of ammunition in safe conditions - enough to supply more than one fighter, perhaps several times. Having a lot of live ammo on board would increase the chances of something going off at a bad time.
To continue: this ammunition then needs to be transferred to the fighter, while in flight at speeds of what, say 200 kts? How do we do this? Perhaps some sort of pneumatic tube would work, but only for the small stuff and you would have to make sure it would arrive safely. Transferring whole cassettes of rounds or bombs would need some other means.
OK, so let's say we transfer the ammo with some sort of failsafe on (pins, etc.). So now the fighter pilot needs some means of removing the failsafe in order to use the stuff.
Perhaps the only feasible solution would be a carrier aircraft that could take the fighter on board while refuelling and rearming. That is what they built the Akron zeppelin for in the 1930s (Wikipedia link: https://en.wikipedia.org/wiki/USS_Akron_%28ZRS-4%29). Don't think it would be feasible with modern fighters, though.

Very reasonable assertions as to why this isn't done with manned aircraft. Though it maybe become more palatable with drone aircraft in the future. It isn't in my mind at least safe to send an aircrew up with 20 tonnes of fuel and probably as much munitions.  Unless and even still refuelled after take off, that is one extremely dangerous aircraft on the ramp should an engine lose power or suffer an  uncontained failure.  Ejection of the aircrew at low altitude may not permit time to escape before cookoff of explosives may start if there is fire on crash.

carrier aircraft were tested as late as the 1950s when it was planned to launch F-84s from the bomb bays and in some plans wingtip pylons mounted on modified B-36 bombers in order to provide protection against Soviet interceptors to the bomber force. It was abandoned due to the massive problems involved in safely launching and recovering the satellite aircraft.

Good answer, but I think the most valuable argument is the need. Why would you do that in modern warfare. Dog fight does not exist anymore with the new kind of air air missiles. Bombing? You will have one or more fighter for the mission target. Why taking bomb mid flight. There is no need of that in a fighter mission today.

@ChrisLau I seem to recall "dog fight does not exist anymore" being one of the arguments for not mounting any kind of gun on an F-4 Phantom.  Result?  Externally mounted cannon pod taking up a hardpoint so the aircraft had point defense.

@ZeissIkon In the 60s if the question was already there, I can really understand the need to get one back when you see the other kind of aircraft flying at that time. But in the actual context in 2010's the efficiency of air air missiles are insane in a range of 6nm and still pretty good in the range of 10nm. I'm not sure of the need of the cannon for dogfight. However, for attacking on ground target like the A10 is doing, why not? The french Rafale has still a cannon with 150 rounds only for that.

And yet, at the insistence of pilots, they mounted an internal cannon in the F-22 and (as i recall) the F-35.  There are things you can do with a cannon or machine gun that you can't do with a missile -- say, firing warning shots, or attack targets visually that radar can't lock (vehicles on the ground, perhaps).

Agreed that pilots are insisting on it, I was more looking from a logical point of view. And also agreed on the target on ground that a radar can't lock. But in case of dog fight, I really don't see the point on present days.

Aerial rearming has been a daydream of military tacticians for decades. However, the task is much more technically demanding than aerial refueling, which is in itself a fairly demanding task for pilot and boom operator just to get a 50-foot fuel hose hooked up.
The technical issues include:

Physically capturing and docking a smaller aircraft with a larger one. The USAF tried it back in the 50s with a B-36 carrying a specially-modified RF-84F. In those days there were no computerized flight controls, and docking the fighter back up with the mothership after it had done its thing proved to be more dangerous to the bomber than just running the mission without a fighter escort at all. It would not be inconceivable for modern avionics to improve on that, however the relative size of fighters compared to larger support craft has increased considerably. Here is a KC-135, built on the "Dash-80" airframe that also sired the 707, refueling an F-15C that's not really that much smaller when you look at it:

Placement of most ordinance under the aircraft. Most fighters and ground attack aircraft carry weapons on external hardpoints under the wings (the RAF-variant SEPECAT Jaguar being a notable example of both overwing pylons and the insanity of British aircraft designers):

When in refueling position under a tanker, the aircraft's most deadly weapons are on the wrong side of the jet to try to get to them to replace or reload them. You'd have to either bring the aircraft inside the mothership, or have it land on top (and provide a sheltered work area for a crew to get to the ordinance pylons).
Relative fuselage width of mothership versus wingspan of fighter. The largest fixed-wing craft in the U.S. arsenal is the C-5 Galaxy. It's a big plane (though not the biggest, that distinction belongs to the Ukrainians with the An-225). Here it is with a couple F-15s and a C-130 parked nearby for scale:

Even with a plane this size, able to transport other planes, you can see from the below photo that neither the F-14 being loaded nor the Galaxy is in a flight-ready condition at the time:

I'd be interested to see whether one of the light weight fighters (F-16, F/A-18) might fit with less disassembly (the F-18 might if you folded the wings), but it remains that you're just not going to be able to fly a modern fighter into another aircraft in midair, at least not with any currently-flying airframe combination.
Getting crew access to the plane. If you've ever seen a ground crew loading a fighter for a mission, you know it's a fairly complex process of not only putting the ordinance (which can weigh up to 2500 pounds for large laser-guided bombs) onto the hardpoints, but wiring up the arming and firing circuits for each one, and programming the plane's FCC with the loadout. This requires getting a lot of people underneath the aircraft (it can take two or three people to load one hardpoint especially if the ordinance has to be muscled into place; here's two people loading probably the lightest piece of external ordinance the USAF has onto an F-15C, and it's only two people because they're using a hydraulic loader):

As the aircraft can't be taken inside the mothership (see previous point), the only other possible place for this to be done is on top of the mothership. That means you'd have a crew out on top of the aircraft muscling ordinance into place. That first requires a sheltered area on top of the mothership that the fighter can be docked and tethered to, as there's no way a crew is getting anything done in a 150-knot headwind. The fuselage vs wingspan difference is important here too; you're not going to be loading AIM-9s onto the wingtips of an F-16 or F-18 when the F-16's wingspan is 33 feet while the cargo deck width (a stand-in for the amount of usable fuselage width) is only 19 feet.

In summary, loading/reloading an aircraft is a serious operation requiring a dozen people to do quickly and efficiently. Putting those dozen people, and their equipment, and all the ordinance into a mothership, getting the fighter to safely approach that mothership and touch down on top of it, then getting the crew into position to remove expended hardpoint pylons and reload new ones, then getting the plane to safely get back off the mothership... It's just not gonna happen with any current technology.
There was a proposed design for a twin-fuselage C-5 as a shuttle transport aircraft; the idea was that this aircraft could be used instead of the risky crane system to pick the shuttle off the ground at an alternate shuttle landing site like Edwards AFB:

An aircraft of this scale might, might, be able to support an aircraft coming in between the tails, docking, then using remote arms to load ordinance. This aircraft would, by wingspan, be the largest plane ever to fly, and would compete closely with the An-225 on every other size stat except total length.

It might be technical possible with an airship or the Airloader 10.

Airlander 10 flies too slowly for a tanker-style capture of a jet (top speed 80 kts, about 2/3 the standard approach speed of most U.S. fighters), and its weight limit is 10 tons (not sure if it's tons or tonnes; the design is British). An F-15E, completely empty, weighs almost 13 metric tonnes, about 14 short tons. The F-16C/50 is just barely light enough empty to be supported by the Airlander, and if the point is to re-arm it, its MTOW from a land strip is about 18 tons (17 tonnes) so the airlander, to have the ammo for just one F-16, would already have 8-9 tons cargo.

The Jaguar just continues what had begun with the Lightning, and the reason is more the paucity of possible wing stations than the insanity of the British aircraft designers. But I have to agree with your assessment: In my experience, there is really a sizable chunk of insanity in the British aircraft industry, but it is more concentrated in management and the government bureaucracy.

How is the Jaguar an example of any sort of insanity?

@Sean How many other countries can you name off the top of your head that have put weapons hardpoints on top of the wings?

@KeithS: That's not insanity, that's ingenuity!

"The insanity [read: ingenuity] of British aircraft designers" ... <3-ing this ... got some more examples for us? :-)

In short: No, there is absolutely no feasible way of integrating midair rearming with our current equipment.  This would require a retooling of every pylon in existence to fix a problem that, frankly, doesn't exist.
The actual long answer is far outside the scope of this question and involves explaining the intricacies of the pylons to include thing like arming wires, sway braces, and a whole litany of other insurmountable problems that current technology cannot address.  And that's if you could even find a reliable method to transfer a 500 pound piece of concrete from one aircraft to another.  Hit any turbulence and that bomb becomes an inert wrecking ball that is sure to do damage in the 100,000's.

Others have clearly described why this isn't done today.  But we should be clear about why aerial rearming is such a big deal and why it is likely to happen eventually.  A drone airforce has its weakest link in the airstrips or aircraft carriers that it requires to operate.  They have to be close enough to the battlefield to allow sorties to be rapid.  Currently aircraft carriers are a primary solution to this problem, but it is no secret that they are extremely vulnerable to anti-ship missiles.  A drone airforce that could automatically transfer fuel and ammunition becomes very powerful and scary.  A swarm of attack drones with tending drones that can operate within 100 miles of the battlefield become much more powerful and flexible compared with an aircraft carriers who must stay in deep water and whose stand-off is increasing steadily as anti-ship missiles improve.  Imagine transport and refueling aircraft that could replenish the tenders, and you have a fully automated supply line that can extend anywhere around the globe.  What is more, it is quite survivable because each piece has a backup.  You would have to take out many transport or refueling aircraft rather than one or two aircraft carriers to take out the system.  Science fiction movies have used this arrangement for a long time.   Earlier answers have explained why this is very hard using existing technology.  But with Tesla building systems that can automatically replace a battery on a car, it should be possible in the not so distant future.

This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review

@RalphJ While you are right in the literal sense, this answer contributes a different and in my eyes valuable view to the discussion. If the weapons are adapted for enroute re-arming, we might see more chemically-powered directed energy weapons and the like.

@PeterKämpf this is not a forum, we don't have discussions (outside of chat), we have questions, and answers to those questions

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Why do forward-swept winged fighters have the main wings in the back?

These are the only 2 fighter jets I know of with forward-swept wings. (Su-47 and X-29, they're both still experimental). As you can see, they both have their wings in the back, not the middle.
Why is this? To me it seems like those wings in the far rear place the center of lift very aft, meaning a constant nose-down torque.
Is there something precluding a conventional-tailed aircraft with forward-swept wings?

Becuase it looks absolutely bad ass.... no? That's not the reason? :)

Also, they're not both "still experimental", they're both cancelled.

The X-29 was never a fighter jet, nor was it ever meant to be. It was a test platform for NASA. The SU-47 has a similar role, although more geared towards military applications, only 1 SU-47 was ever built, and I'm not sure you can consider it a "fighter" since I don't believe it was ever loaded with weapons.

@RonBeyer I think the term "experimental fighter" can still apply. AFAIK, the main reason for exploring the forward-swept wing in both of them was for the agility of a fighter. They are/were prototypes, which don't necessarily need weapons at the early prototype stage.

Technically they are "technology demonstration platforms", the technology demonstrated on both was to be used in other aircraft. Here is a good read on the X-29 program for anybody else who is interested, and has time to read 340 pages

These are just two canards with forward-swept wings. There is no general rule that the wing has to be in the back once it is swept forward. In both particular cases the configuration was selected to achieve the highest degree of agility possible. If you command a pitch-up in a conventional configuration, you first need to decrease lift in order to achieve your eventual goal to increase lift. In a canard, however, a pitch-up command achieves a lift increase immediately.
To prove my point that conventional configurations can also be forward-swept, here a few examples:

The first big forward swept aircraft, the Junkers 287 research airplane (picture source). The odd engine placement was the result of optimizing the cross section distribution for transsonic flight (what is today called area ruling). The white spots are pieces of sticky tape to attach wool tufts for flow visualization, and the canisters below the wing engines are rockets to shorten the take-off run. The aerodynamically shaped canister on the tripod right ahead of the vertical tail houses a film camera for tuft observation in flight.

Here is a real oddity: The Akaflieg Berlin B11 forward-swept tailless glider (picture source). It was never completed because the center of gravity turned out to be too far back. Also, the stall characteristics would have been - how should I say - interesting.
Most two-seater gliders use a slight amount of forward sweep to place the rear pilot at the center of gravity, so the plane can be flown by a single pilot without the need of adding ballast.

The HFB-320 Hansa Jet was more successful, and here the forward sweep was selected to keep the cabin free of the wing spar (picture: Eric Tammer / source: PlanePictures.Net). However this configuration was not trouble-free, either.

I think the reason that the wings of the fighter jet are in the back is that this creates the shortest arm between the c.g and the location where lift acts. The reason you see fighter jets with a forward sweep is that they increase the maneuverability at high angles of attack.

"Tailless" means no horizontal stabilizer? The Akaflieg Berlin B11 seems to have a vertical stabilizer, at least.

@DavidRicherby Yes, that is the idea. It is not a pure flying wing.

@Brilsmurfffje: Yes, the aeroelasticity of a forward swept wing helps in agility. We have that covered in this question. The cg is always close to the wing because it creates most of the lift.

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Could someone really die in the way that Goose did in the movie "Top Gun"?
Looking at this question I remembered a question I always wanted to ask:
In the movie "Top Gun" one of the main characters dies when trying to eject from the F-14. Here is the scene where this happens. Did an incident like this ever occur in real life, or is there at least a theoretical possibility that a pilot could be killed this way?
Top Gun was filmed in the mid 80s, which is quite a while ago. If there were incidents, did they do something to fix that issue? And this question goes not only for F-14s but also other aircraft with ejection seats.

See Ward Carroll's take on the question (he was an F14 RIO like Goose) - https://www.youtube.com/watch?v=LwS1k8LKxJg

Some sources I found claiming the event was real:

A flat spin creates a low-pressure area and stalls the canopy when
ejected. Producers wanted a midair crash but based this accident on a
real-life incident instead.

(source)

The way Goose died was actually based on a real life incident that
happened to a 14 crew in the Navy. Don't remember the specifics, just
found this out recently while reading an article in one of last months
flying mags (not Flying)

(source)

I have a photo of the 'real' Goose and it's true that he died of seat
ejections but not exactly like the movie.

(source, with pictures)
There's also an interview of Steven C. Schallhorn, who apparently was one of top gun instructors interviewed for the movie:

Dr. Schallhorn said during his interview for the movie, he explained
how a flat spin could actually happen with an F-14 and that it
complicates ejection. "The aerodynamics of the F-14 flat spin affect
the timing of the ejection sequence," Dr. Schallhorn said. "The canopy
is jettisoned, followed by the ejection of the back seat, followed by
the front seat. In a flat spin, the canopy, when it ejects, bobbles
for an extra few hundredths of a second above the aircraft. That
upsets the carefully engineered sequence because the guy in the back
could then hit the canopy. That sequence made it into the movie."

(source)

I second this.  I know some 14 drivers that echoed the same opinion.

This is excellent! When I saw that scene, I thought it was impossible, as the front of the canopy normally blows first and then the rear, so that it is completely thrown clear before the seat ejects.

Welp, shoulda put a couple Sepratrons on that canopy...

Is it possible to spin from the desert out to sea?

I was a pilot in the Tomcat for 1,800 hours 1975-85.  We actually had a written and memorized procedure that when ejecting from a FLAT SPIN you did not just pull the ejection seat handle(s).
The canopy was to be MANUALLY "jettisoned" FIRST via the Canopy Jettison handle.  AFTER doing so, you THEN reached for the seat ejection handles and pull to eject.
Those couple of seconds to get to the ejection handles after the canopy jettison gave the canopy time to clear the area overhead the cockpit since the aerodynamics of the flat spin (going straight down while spinning like a frisbee) could cause the canopy to "hover" over the cockpit area briefly.
Otherwise, simply pulling ejection handles only means the backseat immediately followed the canopy in firing only a half second after the canopy left in a normal ejection sequence -- risking the back seat hitting it (like Goose).  The manually jettison first procedure was SPECIFICALLY created in our manual ("RIO... jettison canopy, then command eject") to avoid the fairly good possibility of the back seat hitting the canopy actually happening (along with possible pilot incapacitation).

I don't think it's going to get much more authoritative than this. Thanks for the answer and your service!

This question has been asked before on the Net, and there are some who say it happened once in advanced training operations. Unfortunately, I found no detailed reference.
For the likelihood of the events which lead to the ejection sequence, see this question.
The ejection sequence is at least factually wrong when showing both seats being ejected almost simultaneously. In the F-14, first the backseater (RIO - radar intercept officer) would eject, and the ejection of the pilot would happen 0.4 s later.
The ejection system of the F-14 was certified for 0-0 ejection (on the ground and at rest), and the canopy would be thrown backwards by an explosive charge. In a flat spin, a case not anticipated during development, it is possible that the canopy stays trapped in the turbulent, separated flow above the airplane, and then the first seat to come out has a chance of hitting it. At least this detail is not impossible.
Ejection is a violent process, and limbs have been dislocated and/or broken, and pilots have been knocked unconscious during ejection. Hitting the canopy in a still accelerating seat could indeed knock the seat's occupant unconscious.
This was fixed at least so far that a technique was developed to end the flat spin of an F-14. For other aircraft the system is tested and certified with the aircraft at rest, so hitting the canopy in a mid-flight ejection is impossible when the jettison mechanism works as intended. There have been cases, though, where the canopy failed to separate, and then an interlock would prevent the seat from firing. More modern designs use canopy breakers for clearing the way through a closed canopy, but they work only around the head. I don't want to know how the pilot's knees get mangled form the acrylic (or - even worse - the polycarbonate) when it is their time to clear the canopy.

Well yeah, unconscious, but can it actually kill somebody (I guess in the movie the cause of death was a fractured neck or something similar).

@Maverick283: Yes, I personally know of one case of a fractured neck, but this pilot ejected outside of the seat's envelope, in a strong sideslip. My interpretation of the movie was that Goose drowned when he was in the water.

In the movie it can be seen RIO ejecting first and then the pilot, so isn't it factually correct, actually?

@eis: Yes, but even though it is in slow motion, they both leave the plane almost at the same time. A real ejection sequence would have looked much different.

@PeterKämpf There is only 0.4s between them.  Looks good to me.

@Simon There is only about half a second between firings in the slow motion scene and the seats are not actually powering away from the aircraft. This should look very different in real life.

Near as I know, the answer to the question is yes, an F-14 flight crew could be killed in that type of ejection if the Tomcat was established in a flat spin.  I believe there was one ejection of an F-14 aircrew where one of the crewmembers actually made contact with the canopy during the escape process.  Fortunately he was not injured, but the incident served as the basis for Tony Scott's technical advisors to create the scene.

That .04 seconds is only accurate for the inter-seat sequencing system. If you each pull the handles, you go when you go.

I suspect that no-one here has the expertise necessary to answer this with absolute certainty.  This answer is supposition.
The incident started with a double flame out, precipitated by flying through the exhaust of the other aircraft, following which it entered a flat spin.  In this condition, it would be possible although unlikely that the canopy could remain above the aircraft and the crew member be ejected up into it.
There have been real world incidents of ejecting crew members hitting canopies. I'll come back and edit with links or citations if I can find any.
In the words of Mythbusters, I would say that this myth is "plausible".
Yee hah, Jester's dead.

This is more in the way of a comment regarding the F-4 incident. In 1969 an F-4J launched off the #1 cat off USS Ranger. The plane failed to gain suffiecient airspeed and went in the water. The RIO safely ejected. The pilot was lost. All that was recovered was his shattered helmet. The only possibility is that his canopy did not clear the plane before his ejection. I can provide the log of the incident if so desired. I was serving on the Ranger at the time. I am now the webmaster for Ranger's History & Memorial site. I have the logs for that cruise.

Hi Ranger_Vet, welcome on aviation.stackexchange. It could improve your answer if you were able to provide links with information to this event.

@BogdanWilli - http://www.ejection-history.org.uk/Aircraft_by_Type/F-4_PHANTOM_USA/f4_phantom_US_1969.htm

Looks like the only accident fitting the description was on 02/20/1969, F-4J no,155763 (VF‑21) Stated cause is "catapult bridle separated from the aircraft prematurely". LTJG David Phillip Neisler [Neislar] was killed.

Ejection in general is not a safe thing to do. It's a measure of last resort. For example, the ACES II seat used by most US military aircraft is listed as having a 94% success rate in envelope, and 89% out of envelope (the conditions the seat is designed to handle), the definition of success being that the person lived, often with injuries suffered during the ejection.
And it's one of the safest ejection seats ever made. Earlier efforts back in the 1980's, the time that Top Gun was made, had maybe a 75% success rate. Striking a canopy that was slow to open or other parts of the aircraft on the way out was known to happen. On the US Navy A6, the canopy didn't even open in an ejection - the pilot and seat were blasted through it. During the first Gulf War, the Iraqis put on television an A6 pilot whose face was battered and swollen. That wasn't the Iraqis beating him up, his injuries were suffered during the ejection.
Speed of the aircraft at the time of ejection is a factor... slower is better. If the aircraft is exceeding Mach 1 at the time of ejection, the survival rate goes way down.
So, yes, it's possible to get killed in an ejection. Not something you do unless the alternative is definitely getting killed in a crash.

Not a perfect correlation with the Top Gun scenario, but somewhat relevant.
A mid-air collision between an F-4B Phantom and a DC-9 in 1971 highlighted an already known issue with the F-4's ejection system.  As ejecting into a closed canopy is less than desirable, an electrical interrupt was designed into the circuit to prevent actuation if the canopy was closed.  On the F-4 with its split canopy design, the pilot's canopy would often not unlock if the RIO ejected first, thereby trapping the pilot inside the aircraft.  Modifications to the fleet were already underway but the aircraft in question had not received them.
So although this system was designed to avoid ejecting into the canopy, it led to the pilot's death anyway.

The F14 seats had an interlock that prevents the seats from firing while it is in place. It is attached to the canopy with a steel cable. The canopy being blown away from the aircraft is what will pull the interlock allowing the seats to fire. Again before the canopy lanyard pulls the interlock out the seats will not continue with the ejection process.
I was an AME2 in the navy and worked on ea6bs and f14s as well as the Martin baker ejection seats found in the a6, ea6b, and f14.

Welcome to Aviation Stack Exchange!  Can you please describe what the interlock does in slightly greater detail?  A picture would be great.

Interesting discussion. But one thing that isn't addressed is the time elapsed between the canopy jettison and the first seat to leave the plane.
This is relevant because of the flat spin.
An f-14 is 63' long. If you put the center axis of the spin roughly in the middle that means the pilots are probably half of that distance to the nose of the aircraft, so say 15 feet from the axis.
If the nose of the aircraft makes a full 360 degree rotation every second, that would mean the pilots are traveling around their circumference of the circle at nearly 100' per second. (The nose cone would be traveling at about 200'/s)
That means that if the canopy fires, and a .5 second time elapses before the first seat goes, the pilots should be half a rotation away (or ~50')  from the canopy.
But of course there is the problem of the momentum of the canopy and air resistance.
The momentum of the plane would have been accelerating the canopy at the same rate while the two were attached. However, once the canopy was jettisoned (and we assume the canopy is jettisoned in a perpendicular vector to the aircraft in that moment), the canopy should immediately begin to slow its rate of rotation as compared to the rest of the system.
Turbulent air above the fuselage considered, the canopy should have been slowing it's rate of rotation, even if only slightly. This would create "z-axis" distance between the pilots and the canopy.
Finally, there is the variable of longditudinal acceleration. The same reason why maverick couldn't reach the ejection handles above his head. The rotation would have been creating an "outward" force on the canopy while it was spinning with the aircraft. So when the canopy was jettisoned, that momentum would have carried through and pushed the canopy off the nose of the aircraft. I know people have mentioned that there was a "backward" jettison path designed into the f-14 which theoretically could have exactly cancelled out the forward momentum of the canopy but this would be a very big coincidence.
Anyway, my theoretical conclusion would be - assuming there was some kind of time elapse between canopy and first seat - is that by the time the first seat fired, the canopy should be "lagging" behind the rotation of the cockpit, as well as having been moving forward off the nose of the aircraft, leaving the pilots to clear the aircraft safely.
But that wouldn't make as good movie. :D

welcome to aviation.se. well, that's quite a wall of text. concerning my theoretical conclusion, could you make it less theoretical and more practical (i.e. carry out the computation and have references)?

Hi Federico - it's theoretical because I don't think the data is available to make a proper calculation. However, using the physics and "directional" data as I have above, you can reasonably surmise that the canopy wouldn't interfere in the pilot ejection. Would be a cool experiment though.

Either way, it's still a wall of text...

Short answer: It's entirely possible, but unlikely.
I have no prior knowledge of the F14's engines, nor have I worked on them, so I can't say anything about the engine situation. I do know however, that it is true that these engines could not handle intaking another jets exhaust for long periods of time. These problems have been fixed with newer aircraft like the F15, F18, F22, F35 AND even the newer models of the F14. However, the ejection situation is unlikely. For people discussing the ejection process, it is not simultaneous like the movie portrays. The canopy is fired first with an extreme amount of pressure from the rocket motors located on both sides of the canopy. Explosives located on the rear of the canopy fire beforehand releasing the canopy from the aircraft. The motors send the canopy away from the aircraft in precisely .45 seconds at least 100 feet upwards and to the rear of the aircraft. After the canopy is fired, the ejection process is started. The seats fire directly upward (not anywhere close to the canopy). The seats fire at different times. First the rear, then the front. It is close to impossible, even at 0 airspeed and in a complete spin, for the canopy to remain right on top of the aircraft during ejection. NOW. After all of this, you may think "there is a chance". You would be correct. If for some reason the rocket motors were damaged or were working incorrectly than they may leave the canopy directly above the Aircrew. BUT, they thought of a solution for this too. Canopy bracers. They are built into the top of the seat and activate on ejection. Two bracers are designed to puncture or stop the canopy from getting too close to the Aircrew.
So technically speaking anything is possible but there were and are so many safety features built into Aircrew ejection that it is highly unlikely. However the engine incident was a problem with the early models of the F14. This is fixed with newer aircraft.

This answer would be greatly improved if some sources / citations were provided.

This seems to be in direct contradiction to this answer from an 1800 hour F-14 pilot. A guy who, one might think, does have knowledge of the F-14's engines and ejection system. Unless you've can share references stating what and how things have changed since '85, his answer carries a bit more credibility than yours.


text:
Could the Cruise-Efficient STOL configuration be as efficient as a conventional airliner?
The Cruise-Efficient Short Take Off and Landing (CESTOL) is a NASA project.  There is a video here:

The configuration is a conventional fuselage at the very front of the aircraft with enormous thick section leading edge extensions.  The wings outside the LEX appear to have similar aspect ratio to a 737 or A320.  The aft fuselage is flattened and there is a v-tail.  The engines are buried in the wings in a fashion similar to the Gloster Meteor aircraft.
How much less or more efficient would this configuration be compared to a conventional tube and wing configuration for a 737/A320 size aircraft given similar engines and materials?

Without data, it is not possible to tell if one design will be better than another. This is because it is one thing to make a concept (which this is) and entirely another thing to manufacture and operate the aircraft (like A320/737).
Actually, the design in the video is not entirely new, It is similiar to the Boeing YC 14

developed for UASF AMST program. It is instructive to note what happened in that program.
The AMST program was initiated for developing a tactical STOL aircraft, requirements similar to the CESTOL. Even though YC 14 met the requirements, the program was scrapped for other reasons and the C17 was developed from another contender in AMST program, the YC15.
Even during development fo the YC14, the drag was more than expected and Boeing struggled to bring it under control.
However, I doubt the design as shown is ever going to be made into an actual aircraft. There are too many problems at first glance

The wing seems to pass right through the fuselage. This is not going to work in a transport aircraft.
The location of the engines suggest that the main spar will pass right through it. This will have strength implications.
In case the aircraft is used for STOL operations, the rear fuselage design should be redesigned for preventing tail strike as the landing gear in all probability will be shorter.
Putting the engine inside wing is not a great idea as it increases complexity and chances of catastrophic wing failure.

There are a number of similar programs for developing efficient STOL aircraft, none of which have come into fruition. It is going to to be the economics of the operation from small airports, rather than the aircraft itself, which will decide if these designs will ever see the light of day, let alone operate in commercial routes.

If the design has so many issues, why was it released by NASA?  Shouldn't they be trying to provide quality designs that might prove useful?

They have not released anything. It is  just a concept. As part of its research, NASA releases a number of concept aircraft, which are rarely made. Usually, the aircraft manufacturers just incorporate some useful technologies from these concepts (like supercritical airfoil etc.)

Besides, small-airport operating economics favor fuel-efficient turboprops anyway -- aircraft like the DHC-6 are simply too good on that front to pass up just because some people have this vague notion of "jets good, props baaad"

Another thing to note is that the basic concept of the YC14 is practical -- the Antonov An-72 uses that layout as well to good effect.

@BrinnBelyea NASA’s mission is research, not producing commercially useful designs. Sometimes it is interesting to see if a certain idea is as bad as you think it would be, because sometimes we’re wrong and learn a lot from that.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How are anti-aircraft missiles tested?
How are anti-aircraft missiles and counter-measures tested?
When they design an anti-aircraft missile, how do they test it so that it actually locks on to a target and destroys it? Do they simply fly a plane in the air and then fire a missile at it and have the pilot eject?
Similarily, how are counter-measures tested? Do they fire a missile at a target and check whether it misses?

See http://www.rense.com/general20/fail.htm for an example description of a test (and yes, these tests fail; that's why they do it...)

You don't want to ask how no-tears shampoo is tested!

On enemy aircraft :-(

The short answer is that the final qualification tests are done against drones like the QF-4, which are converted from retired F-4 fighters.  These tests are still extremely expensive, into the millions per aircraft destroyed, so there are many dry runs and non-destructive tests completed beforehand.  Sacrificing a target drone isn't done until the project team is very confident of a positive result or they are unable to obtain necessary data by other means.

This is the original use-case for which the term "drone" was coined. I believe it was by the US Navy. The original aircraft which were called "drones" were RC planes with no autonomous capabilities and no cameras.

As a quality assurance professional, I can tell you that adding or removing humans changes the test drastically. Of course, adding humans to the test would change the cost of the test drastically and the ethics slightly.

Here is a video of an AIM-9X being tested against a QF-4.  https://www.youtube.com/watch?v=4g4_jzqBJnA  In some other videos the drone actually has countermeasures deployed.

Let's not forget the Ryan Firebee.

They will also use MQM-107, BQM-34, BQM-167 drones as well.  And use the VDOPS system to get all the data on the missile performance. And before going to the range, they will do hardware in the loop testing at places like the GWEF at Eglin.

@corsiKa: What, only slightly?

@slebetman  I think you will find that target drones existed long before that - the originals were gliders, or earlier still just a flag, hauled along a 'safe' distance behind a standard aeroplane of the day. Piloting the tug was not a job for the faint-hearted!

A large part of the complexity of any missile is in propulsion and guidance. The warhead isn't trivial, but in comparison that's not the hardest part. This means that in testing, you can often replace the warhead with a sensor package. This applies both to missile development and counter-missile development.
Missile warheads additionally can be tested on test stands, without being launched first.
This just leaves an integration test where missile and warhead are tested in combination, and for that Brian's answer applies.

They also conduct many tests using towed dummy units. (TDUs)  These will often be small in physical size but have radar reflection or heat generation to allow it to look like a normal aircraft to the missile.  Much less expensive to destroy.  The missile will also have a failsafe using the IFF technology so that it does not attack the towing aircraft, and an additional failsafe that the missile can be destroyed manually.

I begin with the premise that there are generally 3 different types of anti-aircraft missile systems. These are
(a) Man-Portable Air-Defense System (MANPADS) also called Very Short Range Air Defense Systems(VSHORADS) for example RBS-70 , Verba , Starstreak ,
(b) Ground based Medium-Range Surface-to-air missile systems for example BUK-3  and
(c) Long Range Air Defense Systems  for example Patriot MIM-104 and S-300V.
Now , the testing of these 3 different types are obviously different , however the cornerstone of these tests regardless of the type would include :
(a) Digital Simulation of launches - almost a million launches are simulated ;
(b) Hardware-in-the-loop simulations – thousands of  tests for each system
with actual missile seekers and jammers
(c) Flight Tests simulation
(d) Functional configuration audit to verify compliance with system functional requirements
(e) Live Fire tests - carried out on unmanned aerial vehicles that serves as targets
https://sites.google.com/site/samsimulator1972/home
There are generally 3 main parts in a missile .
(1) The rear section contains electronic packages , a battery and the rudder mechanism
(2) The central section contains the sustained motor and wings
(3) The forward section contains electronic packages , the gyro and warhead
Therefore , Tests have to be conducted at  the component, subsystem, or system level as well .
Missile Sub sections
Countermeasures for air defense systems are categorized into active and passive systems.
(1) Active countermeasures are for example flares and directed infrared countermeasures (DIRCM)
(2) Passive countermeasures include infrared signature reduction, fuel tank inerting and redundant controls
Tests are carried out for Flares , Chaffs and  Infrared .
The chaff cuts are tested for optimization so as  to provide a broadband radar return .
The various tests carried out on Chaffs are related to their Performance Requirements shown in the image below

A Flare consists of  (1) a firing cap, (2) a powder charge wadding between the charge and the bullet, and (3) a wad at the end that keeps everything in place.  The electrical firing “cap” creates a gas that ejects the plastic or nylon slider, 2 felt spacers that hold everything in place, and the end cap. All these 3 components have to be tested .
For evaluation of effectiveness against two-color systems, an integrated color ratio filter system is used to enable flares and target representation to contain the appropriate
amount of energy in each spectral region of interest .

authors: Bob Jarvis - Слава Україні


text:
Why/How is the B-52 still in service?
The B-52 was introduced in 1955, and is still used by the US Airforce, and is expected to remain in use till the 2040s.
On the other hand, the A-4 Skyhawk was introduced in 1956 and retired in 1998/2003.
Now granted these are completely different aircraft. What I'm wondering, is why one aircraft can remain so useful for so long, while others quickly become obsolete.

Two words: Good enough.

But it will be replaced by the F35 soon enough.  (sarcasm)

The only thing unfortunate about the B-52's in the fleet is that their engines are very inefficient by today's standards (approximately 30% less according to the article).  Fortunately, it would appear that the AF is looking at fixing this exact problem: http://www.defensenews.com/story/defense/show-daily/afa/2015/02/12/b52-engine-private-public-partnership/23185827/

The Tu-95 "Bear" and the German MG-42 / MG-3 immediately spring to mind. Sure we can make marginally better today, but those babies are there, and we know everything that might be wrong with them, as opposed to new designs where we might not know what's wrong with them at first. (Like the F35. :-D )

BBC article - "How does this 1950s behemoth survive in the era of drones and stealth aircraft?"

@jjack why are you asking that question here? Why ask me specifically?

The A4 actually had a pretty long service life compared to some other jets of the same vintage. For axample the F100 was in service 54-71 and the F101 57-72. Israeli Skyhawks were operational as recently as 2012.

Three reasons:

The B-52 stayed useful by taking on "easier" roles as it aged.

It actually started life as a high-performance penetrator, relying on speed and altitude to stay safe. Think Early Cold War, shortly after WWII.
When ground-launched missiles improved, the B-52 was forced into flying low-altitude penetration underneath radars (a role for which it was NOT designed and rapidly wore out the airframe) accompanied by a host of other aircraft to protect it and help it penetrate defenses. Despite their escorts, we lost low-dozens of B-52s in Vietnam.
Later in the Cold War, the B-52 was completely outmatched by air defenses (fighters, SAMs, etc), and had little hope of penetrating defenses (at either low or high altitude) to drop nuclear bombs. Instead, it was relegated to flying in friendly/neutral airspace, lobbing long-range nuclear cruise missiles into the Soviet heartland (a tactic they feared more, as it turned out, than manned low-level penetrators). It was basically a missile bus.
In the Gulf War, the B-52 only flew after air defenses had already been defeated by other aircraft (F-16s, F-15s, F-111s, etc). It was basically a bomb truck.
During ALLIED FORCE (1999), "B-1Bs and other conventional (non-stealthy) aircraft could not survive in the face of double digit SAMs, even when employing advanced decoys and other countermeasures."
The B-1 program, btw, went through a similar progession, starting out as a high-performance penetrator,  then forced into even lower-altitude penetration, then also relegated to bomb/missile trucking, pushed back by AAA, MANPADS, SAMs, look-down shoot-down radar, improved Soviet interceptors, and Soviet AWACS. In fact, the B-1 and B-52 fly largely* the same missions today.

*There are some important differences. The B-1 is no longer nuclear capable (START compliance), leaving that mission to the 20 B-2s and ~40+ ALCM-armed B-52s. The B-1 can also reposition more quickly, lending it to CAS role: it dropped 37% of the then-total ordnance on ISIS (2x that of the A-10)(see source) in OIR before they returning stateside for upgrades and were relieved by B-52s. (And, yes, the B-1 does CAS.)
Overall, the B-1s fly ~330-450 hours/yr, the B-2 ~230-290 hours/yr, and the B-52s ~200-220 hours/yr (2008-2012). The B-1 and B-52 cost roughly the same per hour (the B-1 has higher fixed costs but lower operational CPFH).

In 40 years, the B-52 went from being the US' primary strategic tool against another superpower to being outclassed by small nations.
Bomb/missile trucking is an "easy" job, but far from ideal. You can't bomb your targets until the air defenses have already been defeated---after the "first week" of a war, the most critical phase, when you need them the most. In other words, the B-52 (and B-1) are relatively easy to shoot down, so they're not nearly as useful as they used to be. You can't fly them unless many of the toughest enemies are already dead. So you can't use them as often as you want.
@MSalters phrased it quite nicely: the reason the B-52 (and B-1) hasn't changed is because other aircraft are doing the hard work for them (tearing down enemy defenses), and such aircraft have advanced immensely. But that amount of support is quite resource intensive, so if you wanted to fly B-52s in the "first week" when enemy defenses are still effective, you'll need a lot of help: (Image source: Beyond the "Bomber": The New Long-Range Sensor-Shooter Aircraft and United States National Security - Lieutenant General David A. Deptula, USAF (Ret.), 2015.) The same was true with strike packages during Desert Storm, eg only a third of the aircraft dropped bombs while the rest provided support (jamming, anti-radiation, top cover, etc).

We didn't build enough B-1s and B-2s to replace it, so we kept some B-52s to fill in the gaps (we don't have any other suitable heavy bombers in inventory, this is the only choice).

The 100 B-1Bs were just a stopgap until the B-2 showed up, of which we meant to build 132 (cut to 21 airframes). Had the Cold War continued, the B-2 would have comprised the bulk of today's bomber force.

We were busy buying new fighters and cargo planes.

The official, stated goal is to recapitalize the entire bomber fleet (less the B-2) because it's increasingly obsolete. That's worth repeating: the B-1 and B-52 are near obsolete. They're not nearly capable enough. The next bomber isn't another B-1, B-52, or modded 747 because we don't want to maintain the same capabilities. We want more capability--much more--than what we currently have. We've only waited this long because replacing the airlift and fighter fleets took priority.
The LRS-B (new stealth bomber; formerly NGLRS) will replace the B-52 starting around next decade. The contract is expected to be awarded very soon. The Pentagon briefed a select group earlier this month. Looks very promising---well managed, on budget, very capable, and surprisingly mature.

UPDATE: The B-21 (ex-LRS-B, ex-NGLRS) was indeed awarded 27 Oct 2015, a month and a half after this post was originally written. Very little is known, but it is indeed a stealthy bomber (the official render closely resembles the outer mold line of early B-2 iterations before the redesign). And it is indeed on time and under budget by ~9% (APUC = \$511M vs. the \$550M requirement, FY10\$).

In short, we still fly the B-52 today because we don't have a choice, not because we want to.

Parting thoughts:
I want to emphasize that the B-52 did not remain effective in its intended role (penetrating the USSR on Day 1), upgrades notwithstanding.
Yes, the B-52 survived multiple replacements (eg XB-70, B-1A), but not because it was more capable (it wasn't; the B-70/1A went higher/faster/lower/with more payload), but because those potential replacements couldn't outpace Soviet defenses either and so were cancelled in favor of ballistic missiles and cruise missiles... except the B-2, which could outpace Soviet defenses but was curtailed when those Soviet defenses disappeared. The B-52 survived basically because of luck: against the XB-70 and B-1A, it was the incumbent, already bought and paid for; against the B-2, history smiled.
Also, the B-52 did not "survive" the B-1B. The B-1B was never meant to replace all B-52s in the first place. The B-1B was meant to fill an urgent requirement as a stopgap from ~1985-1995 until the B-2 could enter service. Unlike previous B-52 would-be replacements, B-1B production was not cut short: 100 were ordered, and all 100 were delivered, essentially on time and on budget (though that was actually partly the problem).
Thankfully the B-52's range and payload kept it productive during its long service.

Some background.

The USAF operates ~160 bombers:

76 B-52s
63 B-1s
20 B-2s

A good write-up, especially in view of LRS-B's (eventual) advent.

The LRS-B is well managed, on budget, very capable, and surprisingly mature? What sort of alien technology is this built with? Those adjectives haven't applied to a US military aircraft program since, what, the SR-71?  /snark

Nifty graphic. Please note your source on that.

@freeman Probably since the P-51, which was nicely under-budget, well managed, mature, capable and even delivered in record time. Possibly since the British paid to develop it.

@JonStory: P-51 being "capable" after the British provided it with a proper engine. ;-)

The P-51 was capable before that, just not at the role it later excelled at, but yeah I suppose it was probably more British than American in the end, as a project :p

Had the Cold War continued, the B-2 would not have comprised the bulk of today's bomber force, as the United States would have been bankrupted had they attempted to do so.

It's worth digging into the details. The B-52H, which is the model in service today, was not built in the 1950s but the early 1960s (which, I admit, is not a significant difference).
The key, however, lies in the upgrade programs that have happened constantly since the design first hit front lines. It's had airframe life extensions, avionics upgrades, and weapons systems changes around every 10-15 years, with the latest round happening in the last five years.
That's the how. The why is that it just happens to be damn good at the roles it is given. It's also highly reliable despite (because of?) its age, and as of around ten years ago was not excessively expensive to fly:

The B-1 averaged a 53.7% ready rate and the Northrop Grumman B-2 Spirit achieved 30.3%, while the B-52 averaged 80.5% during the 2000–2001 period. The B-52's \$72,000 cost per hour of flight is more than the B-1B's \$63,000 cost per hour, but less than the B-2's \$135,000 per hour.

Ultimately it comes down to the fact that properly maintained aircraft seem to have shockingly long service lives. There are still 1930s-era DC-3s and C-47s still flying scheduled freight service in Alaska.

I imagine designing and constructing a B-52 equivalent today might cost several orders of magnitude more per aircraft than the B-52 cost in the 50's and 60's, even if you include all the refit costs.

Agreed regarding the service life of aircraft. The PA-28-140 I've been flying was built in 1970 and certainly designed well before that. It's not at all uncommon to see planes built in the 1960s in GA.

It's probably also worth adding that the US seems to find itself in a lot of cases recently where the sophisticated high-speed missile-dodging radar-avoiding ECM-deploying capabilities of the B1/B2 are just not necessary.

Not only is it good at carrying out the jobs its been given but it's supposed replacement, the B1, while good at doing what it was designed for, couldn't do all the things the B52 could. The B52 is just a very good, flexible, general purpose, non-specialist design that can cover a very wide variety of missions.

"which, I admit, is not a significant difference" - It is when you consider that it allowed the B-52H to use the more powerful and efficient JT3D turbofan rather than the anemic, thirsty JT3C turbojets used by the earlier B-52 variants.

The B-52 is nothing more than a massive bomb-truck, so it doesn't need a whole lot of improvements. If it ain't broke, don't fix it. It's not pretty, fast, stealthy, or smart. It's a vehicle to get a whole lot of bombs from point A to point Boom.
Did you know the USA military still uses the M2 Browning machine gun from WWII?
B-52s are great when you want to say "F--- you and everything within 5 miles of you".
I leave with an old saying:

Cluster bombs from a B-52 are very accurate. They are guaranteed to hit the ground.

heck, the US military still uses the M1911 pistol (though it's no longer the official sidearm, select troops are offered the option to use it) from, you guessed it, 1911. Of course those (and the M2s) are not the same ones built in 1911 but new ones produced much later, like a few years ago in case of the M1911s.

Bomb-truck; very good descriptor. The B-52 was originally designed to haul nukes across the Arctic Circle to targets in Russia, but if you can do that, you can haul practically anything a similar distance (much more with the advent of in-flight refueling), from conventional iron bombs to MOABs to cruise missiles and JDAMs, and you don't need all that much in the way of airframe changes. Avionics and engines have been the real areas of improvement for large aircraft, and the B-52 has taken advantage of both.

In 1993 I saw a Marine howitzer with a 1943 mfgr. plate. It was not a static display.

The B-52 is essentially nothing more than a cargo truck today. It's still useful in that role, although it's obsolete by most reasonable standards.
It does help that the B-52 has its engines in nacelles, which simplified engine upgrades. To its cargo truck role, the engine performance matters more than anything. And as an old and simple plane, there's nothing on board which causes expensive repairs. Cargo trucks and the B-52 alike are judged on cost.
To succeed in its role, other planes have to clean the sky around the B-52. Those planes are subject to much more evolutionary pressure. The F-16, introduced 20 years after the B-52 is already outdated in that role. Currently you'd use the B-2, F-22 and/or F-18E/F. Those planes are much more capable of surviving in contended airspace.

So it wouldn't be used to drop bombs?

@dwjohnston: Well, it's a bomber, so yes it drops bombs. But that's a rather unglamorous task: load bombs, fly to target, release bombs, fly back. A cargo plane could do the same. If the target to bomb shoots back, you don't send the B-52 but the B-2. (Or you drop missiles from underneath the B-52, again a glorified cargo plane role)

Are B52 airframes still currently produced?

@shortstheory the last B-52 rolled off the line about 50 years ago. They're still making spare parts and upgrading them at times.

and no, it's not "nothing more than a cargo truck". Maybe there's no real need for the electronics and other war fighting gear except the bombing radar when up against the Taliban, but they do have that gear and I'd not want to be in one if it were to have to go up against the Soviet or Red Chinese armed forces.

@jwenting The 2040 retirement in the OP sounds absurd then. How can a single airframe remain airworthy for nearly a century!?

@shortstheory: A commercial plane has a duty cycle of 25%+. 50%+ is normal. A B-52 spends <5% of its time airborne, and a lot of the other time in maintenance. And presumably quite a few of the flights are without bomb load, so with less mechanical stress. Commercial planes rarely fly empty.

@shortstheory it's the planned retirement date now. And I'd not be surprised if they extend it beyond that, given that there's nothing even on the drawing board to replace it and aircraft development programs for the USAF now seem to take 25-30 years to even lead to a pre-production run (just see the F-35...). It is insane, but that's how DC bureaucracies now work. Where the original B-52 was designed literally in a hotel room on a sketch pad over an evening (of course the details took longer, a few months), we now need decades to do the same using supercomputers.

My personal estimate is that the B-52 will be replaced by a Boeing cargo plane. The P-8 Poseidon is already a ship-hunter based on a 737, using Harpoon missiles instead of bombs. I'd expect the B-3 to re-use either the P-8 platform or be a 767 derivative.

@Msalters Nope, they are looking for a new variant of a stealth bomber. Wikipedia (although not doctrine), shows more information.

@MSalters - this is a poor answer. And the F-16 is not really "outdated" - it pales in comparison to the F-22, but late Block F-16s are still a far better multirole fighter than the vast majority of militaries have

@SSumner - And in fact the U.S. doesn't even operate the "best" F-16; take your pick between the Israeli Ra'am and the UAE Block 60 variants, they both have better capabilities (range, weapons, avionics) than current USAF Block 52s.

@HCBPshenanigans According attendees of a Pentagon briefing earlier this month, the LRS-B will be a very stealthy (likely subsonic) bomber probably weighing between 40-70 tonnes.

@jwenting - There is definitely a program to replace the B-52; see the LRS-B. The RFP was released last year; the contract is expected to be awarded any day now; and the IOC is anticipated for ~2025. Modern fighter a/c take ~20 years to develop (see: Rafale, Eurofighter, Raptor, F-35)

@HephaestusAetnaean there have been programs to replace the B-52 for decades. The B-1, the B-2, several others. None went anywhere much. Given the death of the US military budget I can predict pretty reliably that this one will not go anywhere either.

@jwenting - "The B-1, the B-2, several others. None went anywhere much." Eh? The B-1 and B-2 did replace a number of B-52's; in fact, they comprise the majority [and most capable portion] of our bomber fleet.  B-1 production was cut short because of changing threats/requirements and the upcoming B-2; B-2 production was cut short because a 45-year long war ended; ie, the B-52 survived because it was in the right place at the right time--it is not inherently an ideal platform. By all indications, the LRS-B looks very promising---well managed, on budget, very capable, and surprisingly mature.

@MSalters - The LRS-B won't be derived from an airliner. The USAF has repeated stated they want a much more capable and survivable platform [than the B-1 and B-52] because conventional bombers simply cannot survive in the face of modern (or even outdated) air defenses. In other words, they're looking for a stealth bomber, not a new B-52.
The designs proposed by Northrop and the Boeing/Lockheed team are apparently stealthy flying wings (or similar).

@HephaestusAetnaean none went so far as to replace the B-52, the B-52 survived them all... The B-1 only saw 100 built and they're gone, the B-2 only saw 20 built and they're not doing much (being too expensive to risk and too fragile to have them fly into adverse weather). Meanwhile the B-52 at 60 years old has a higher number in service than either of them ever had at their peak AND is scheduled to stay in service past the retirement date of the B-2.

@jwenting - 'The B-2's aren't doing much... too expensive, too fragile.' What on earth? In Serbia they routinely hit 16 targets per sortie. On the opening night against Libya, 3 B-2's destroyed 45 separate hardened aircraft shelters with a single PGM each. The B-1 is both cheaper per flight hour and flies twice as many hours (400+) per year as the B-52 (200+), which requires more maintenance. Again, the B-52 has survived because other programs suffered misfortunes, not because the B-52 itself is inherently ideal.

@jwenting - the B-52... is scheduled to stay in service past the retirement date of the B-2. The B-2's service life extends to 2058. The B-52 (and B-1) are structurally able to fly til 2044... but it's dubious they'll be able to carry out their missions.

@jwenting What do you mean by the B-1s being 'gone?' It looks like they're right here. They recently one-upped the bikers at Sturgis in terms of exhaust noise. - lol

The military won't even derive a wrench from a commercial one, for crying out loud. A boeing engineer once told me how the USAF wanted a hand tool w/ some special flange-thingy, not absolutely necessary for the job.  After all the procurement requirements, overhead, and low production run we're talking $600 for a $30 tool.

@HephaestusAetnaean: "B-2 production was cut short because a 45-year long war ended" - the end of the Cold War merely provided a convenient excuse for something that would have been forced on the U.S. military in any case by the need to avoid bankrupting the country.

The B-52 is still in service due to its high degree of effectiveness. It is not the only plane still in service by means of effectiveness. Other aircraft, such as the F/A-18 Hornet/Superhornet, F-16, F-15, E-2C, C-2, C-130, and UH-1 are still in service because they are still very effective and it would be cost ineffective to replace them. It was anticipated that the F-35 would replace the F/A-18, but after the 3 trillion dollar price tag for the program, and the fact that in test runs against F/A-18 Superhornets and E/A-18G Growlers the F-35 was greatly outperformed, the Department of the Navy decided they will not replace it until around 2035. The B-52 is still very effective for bringing heavy tonnage of explosive ordinance and forcing the hostile force into surrender. If it isn't broken, don't fix it.

Howdy, and welcome to Aviation.SE! I certainly don't disagree with your answer, and with some supporting evidence (links to Pentagon/3rd party studies with some relevant quotes in your answer would be nice), it will make a nice addition. As it stands, it doesn't add much to the answers that are already here. Please be sure to take the Tour and browse through the rest of the Help section to familiarize yourself with the StackExchange Way™ of doing Q&A vs most boards free-form general discussion.

Excellent points. Simply put, the B52 is cost effective. Ghost Rider is an example. One of our B52's was damaged, so Ghost rider will be retrofitted (from mothballs), for $13M. The military's decision to upgrade electronics and weapons systems in all B52s shows their reliance (and confidence) in the aircraft. http://www.dodbuzz.com/2013/07/12/air-force-begins-massive-b-52-overhaul/
It's impossible to cost justify replacing it (the tried) so BUFF keeps flying.
It is not stealthy, but don't underestimate its ability to jamb signals. Even using non-powered bombs, from its altitude, glide bombs can be released 60 miles from target.

Well, all aircraft are upgraded as they age to keep them relevant, not just the B-52. They also cost more to fly per hour than the B-1, a younger and more capable platform. It's relatively easy to justify replacing them---they're old and near-obsolete (can't survive in the face of even out-dated air defenses)---that's why they're scheduled to be retired first when the new bomber (the LRS-B) enters service.

Couple of other reasons:
It's paid for. Sure, the Buff's engines are not that efficient, even after being re-engined with turbofans, but the cost of the extra fuel isn't anywhere near the $100-150 million it would cost to replace the B52 with a Bone, or the half billion that a B2 costs. You can buy a lot of JP4 for that sort of money.
We bought a whole bunch of them. Final production was 742, which is a lot of heavy bombers. Why scrap them and blow money on a replacement, when they still work? The 50 or so B52's still in service have a huge inventory of spare parts to draw from.
The conflicts the Buff is used in now tend to be lower intensity, with lower threat to the aircraft. Why use a half billion dollar B2 and risk loss from operational problems, if the opponent doesn't have radar to detect the incoming bomber, or SAM's to do something about it even if they do detect it coming in?
The maintenance procedures were worked out decades ago, so no surprises there. Yes, it has a bleed air system known to be a nightmare, but service is well documented, and fairly inexpensive. The B1 has a swing wing, which can be rather pricey to maintain.
It is very tough. It's predecessor, the B47, was quickly retired when low altitude flying caused cracks in the wing spars. The Buff can fly at low altitudes without suffering that problem. Low altitude characteristics became critical when Soviet SAM's made high altitude bombing a very dangerous occupation. With a very strong airframe, B52's can take a lot of hours of flight without serious decay. There is a well documented video of a B52 minus most of its horizontal stabilizer, that sheared off in flight due to excessive side loads. It was landed without further damage.
For many years, NASA operated a pair of early B52's, tail numbers 002 and 008, with the original and very inefficient turbojet engines. Reason? Those engines perform better at very high altitudes than turbofans, and the NASA B52's were used for research and launching test aircraft at very high altitudes. The last one, 008 was finally retired without many hours on the airframe, still sporting a cutout section on it's starboard wing flap, put there to accommodate the X-15's tail when it was being hauled aloft for launching.
Due to that cutout section, 008 was always landed without flaps. (would have produced asymmetric lift) That must have been fun...

"well documented video of a B52 minus most of its horizontal stabilizer" It was the vertical stabilizer.

One small issue. No B-52 has been re-engined, yet. The H models were built at Boeing with the TF-33 fans. (The Gs had J57 turbojets.)

The B-52 is slower, less survivable, more expensive, and can't carry anywhere near the payload of a B-1B. In fact, it can only carry 56% the bomb weight of the B-1B.
With the removal of the AGM-129 ACM from service, the B-52 no longer has any capability to deliver nuclear weapons into airspace defended by modern SAM systems.
So why is it in service? Likely political considerations concerning base closures.

"Likely" in the sense that you can back that up with actual facts and maybe a citation or two, or "likely" in the sense that it's your own personal opinion? The personal opinion of some anonymous person on the internet isn't worth a whole lot without something to back it up.

Also, Wikipedia (not infallible, I know) dramatically disagrees with your claims about payload, saying that a B-52H can carry 31,500kg of bomb and a B-1B 34,000kg. So the B-52 carries 93% of the bomb load.

Wikipedia states that combined payload of B-1B is 56,700 kg. 34,000 kg is the internal payload capacity.

@user22620 and no B-1B would be sent into combat on a deep penetration mission (which is what it was designed for) with external stores. Those were never seriously intended to be used in anger.

@jwenting I'm comparing the B-1B to the B-52 in the role the B-52 serves. The capabilities of the B-1B in a role the B-52 can't perform isn't relevant to my assertion that the B-1B can be a better bomb truck than the B-52.

@user22620 the B-1B was never intended to a bomb truck, it was intended to take over the deep penetration mission from the B-52 when the B-52 was no longer capable of penetrating Soviet air defenses.

@jwenting Neither of these aircraft is capable of performing the originally intended mission, so again the point is irrelevant. Can you provide some evidence that B-52 use provides overall cost savings versus decommissioning the entire fleet and accomplishing those sorties with other aircraft?

Sorry, misread your answer the first time around. If you don't mind making a trivial edit, I can undo my down vote.

authors: Νικα Αντρεεα


text:
What is the 'arm' at the rear of the X-29?
In this image of the Grumman X-29, there is an 'arm' just above the exhaust nozzle leading forward and, apparently, attached to the right side of the fuselage. What is this and what is it for?

Source: Wikipedia X-29 Article
I realize this is an experimental aircraft, but it doesn't look like sensors (like the probe off the nose), it looks more like a structure for lifting the plane.

Similar system on a YF-22: What is this red canister on the tail of the YF-22?

Two X-29's were built, and the only difference between the two is that #2 has an externally mounted spin recovery chute attached to the tail. That is what you are seeing in this picture. The chute is packed in the tube structure and the "arms" are structural to distribute load.
Source

The only significant difference between the two aircraft was an emergency spin chute deployment system mounted at the base of the rudder on aircraft No. 2.

Here is a video of the chute deployed
And here are more details from NASA on the chute system
The reason that #2 needed this and #1 did not is that #2 was going to be conducting experiments at up to 67° angle of attack, where entering a spin was much more likely. #1's AOA was limited to about 21° and was considered the "phase-1" flight dynamics platform, while #2 was the "phase-2" platform.

To some extent, I was right, it is an arm for lifting the plane. by its chute, right out of a spin... :)


text:
Why are almost half of the world's helicopters in North America?
I was reading this report and came across the following quote:

North American purchase plans [for civilian-use helicopters] are a significant component of the overall 2017 survey demand, as the region represents more than 40 percent of the current world fleet.

I don't know a ton about the helicopter industry, so this quote surprised me.  What are most of these civilian helicopters in North America being used for?  More specifically, in North America what are the uses for helicopters that aren't common in other parts of the world?  Does this unique demand come mostly from offshore drilling, police, or medical usage? Why don't they use helicopters for those purposes in other countries?

50% of the world's GA fleet is in the US so you would expect to find half the helicopters there. Why the US has such a large GA sector compared to the rest of the world is really the question here - and an interesting one - but there are lots of factors to consider and I don't know if there's a simple answer.

I wouldn't be surprised if the percentage also applied to other light aircraft; North America simply has a great deal of aviation activity.

@Pondlife No user fees, low (or no) taxes, low fuel costs, large unrestricted travel area and economies of scale (lower parts costs, lower hanger/tie down costs, etc). I think the major part of the difference can be explained as "cost", and probably most of the rest of it explained as "regulations". May be worth a new question though...

More car chases! :P

Two reasons I can immediately think of for the large proportion of the GA fleet (including helicopters) being in the US.  First, the US is a rich country; second, the distances to travel are large.  Much larger than, for example, Western Europe.

Why the question is tagged Usa, while the title specifically says "North America"? Did Alaska and Canada got moved south tonight and nobody told me anything? O_o

Cost, Regulation, SPACE, SPACE SPACE!!! And also more "necessity":  the population density outside of major cities is so low that it can make sense to own a plane to go places faster.

@motoDrizzt: When did Alaska secede from the United States?

What are most of these civilian helicopters in North America being
  used for?

As listed below, Medical and Police use are quite common in the US. The Coast guard runs a fleet of rescue choppers and divers along with their boats. Many news stations also run helicopters for traffic and other areal coverage. There is a fairly sizable market for Powerline, Pipe-Line and Survey related work from rotocraft. There is even a case for moving precarious items.
There is of course a large market here in the US for private, owner flown/operated helicopters in the US. This is at least in part due to the lower costs of private flying in the states. The US airspace system is largely funded by taxes on avgas as well as other federal funding and does not have the same user fee structure that Europe has implemented. In other words here in the states you need to pay to rent or own the plane and gas it up but the use of the air is free. In Europe you will have the same costs with an added cost to use the airspace. In Europe you can also expect AvGas prices to be a bit higher across the board. Although many helicopters are turbine based and run on Jet-A.

More specifically, in North America what are the uses for helicopters
  that aren't common in other parts of the world?

Moving people relatively trivial distances... In many places, general sightseeing. If your bold enough, aerobatics. Although many of these uses are also common elsewhere in the world. However due to the nature of aviation laws here in the US, its a bit easier (and somewhat cheaper) to fly small aircraft.

Does this unique demand come mostly from offshore drilling, police, or
  medical usage?

Police and Medical is fairly common around the world. Oil rig transport occurs only in places where off-shore rigs are used/drill (many reside close to the US or Asian shores).

Why don't they use helicopters for those purposes in other countries?

They do, for example the UK has a pretty large helicopter medical effort and there is the WestPac life saver helicopter service in Australia. There are efforts in Greece and many other places in the world for that matter.

"There is even a case for moving precarious items." Another example: https://www.youtube.com/watch?v=08K_aEajzNA

I'd say remote Australian fliers may prefer the higher airspeed and larger capacity of small aeroplanes rather than helicopters.  There's also more open space so finding landing room is easier than in more-dense locations.

@Criggie - I did come across lots of Australian Airplane centric medical operators as well however since this question is mainly about helicopters I chose to omit them.

From some searching it seems flights by aircraft under 2 tons are exempt from route charges in Europe.


text:
Where can I find details on the control surfaces of the F-15C?
Me and my team were working on a short animation and I need precise details on the following if you guys can point me to a website or answer them here it'll save hours off my search cause Google isn't helping much.

The different stages of the flap extension with their degree of rotation.
The maximum degree of the ailerons going both ways
The maximum degree of rudder both ways
The maximum the elevators can go both ways

And as a big bonus can you provide me with the landing gear specs as in how long it takes to extend, retract, open the great doors and so on? Or a video of an actual F-15C retracting and extending would be great. Not one of those mini-prototypes.

Aileron: +/- 20 degs
Horz. tail: 26 deg up, 15 deg down
Rudder: +/- 30 degs
See: https://www.nasa.gov/centers/dryden/pdf/87906main_H-1073.pdf

What about the flaps?

@ReubenX believe flaps are 0 to 30 degrees, but not 100% sure.


text:
What is the meaning of Minimum Flight Weight?
In the Aircraft Flight Manual of the Bombardier CRJ700, the Minimum Flight Weight is listed as 42,000lbs. What is the meaning of Minimum Flight Weight?

Welcome, Takeshi. Could it be that "What is the meaning of Minimum Flight Weight" is a better title to your question?

Do you simply want to know the definition of this phrase and how to ensure its complied with, or do you want to know why the limitation exists?

Thank you for your comment. I'd like to know the definition and why the limitation of the weight. If flight with less than this weight, how harmful is it to operating the aircraft?

Could it possibly be the case that if the aircraft is below the minimum flight weight, then if it encounters a strong vertical or horizontal gust that generates X pounds of additional lift, the resulting acceleration will be so strong that heavy items with lots of inertia such as batteries, engines, etc might be ripped loose from their mountings?  In other words the airspeed - G-load envelope is only valid down to a certain minimum weight and the specified maneuvering speed etc does not adequately protect the plane in turbulence, or if the pilot makes rough control inputs, below that weight?

An example of use is given in this answer. When the MFW is not satisfied fuel ballast must be used.

After little digging found EASA Part 25/FAR 25.25 (same text):

CS 25.25 Weight Limits
(b) Minimum weight. The minimum weight (the lowest weight at which
compliance with each applicable requirement of this CS–25 is shown)
must be established so that it is not less than –

The lowest weight selected by the applicant;

The design minimum weight (the lowest weight at which compliance
with each structural loading condition of this CS–25 is shown); or

The lowest weight at which compliance with each applicable flight
requirement is shown.

So the aircraft has to meet all of its structural and performance design criteria at all approved weights. As you can see from the wording, the chapter it self is quite ambiguous and includes the entire regulation within its scope. This would include for example controllability and gust limits etc. For example, aircraft being too light would lose its controllability in engine failure or might overstress in sudden gust.

Which is not to say that an aircraft would be dangerous if flown under-weight (although it might well) but that the aircraft has been designed and tested to operate safely at this weight.

For purposes of determining minimum design weight:  it is the empty weight + installed equipment + crew + full oil + MINIMUM (not “undrainable” or “unusable” fuel).  Minimum fuel for these calculations can be determined by the manufacturer, or, for modern aircraft it is the amount of fuel used in 1/2 hour at METO power setting, or for older (CAR certified) aircraft, it is 1/12 gallon per max horsepower. See CAR 4a.37(c).

So it's not a limitation?  But see "On the A310 freighter there is a 'Minimum Flight Weight' ie the take-off weight of the aircraft must be at or above this weight to depart.". From https://aviation.stackexchange.com/a/66487/34686  .

This is the weight in an operational condition(with engine oil, hydraulic fluid, unusable fuel in the tanks[maybe also with a specific usable amount like 30 minutes], and some other misc items), with minimum crew. With sufficient ballast, if necessary, to keep the center of mass position and total mass within the design requirements for safe handling characteristics.
In different words, the minimum weight at which the airplane is allowed to fly, with consideration for required equipment, the required position for center of mass, and performance limits.
As an example, by requiring a certain minimum weight there will be more inertia and it may be possible for the aircraft to be certified for more severe wind conditions.

In other words, the least the airplane can weigh when ready to fly (briefly).

Now that I consider the exact words, there may be two meanings. What I described is the minimum operational weight. It is possible the minimum flight weight is a limit on calculated weight and balance, there are a few transport category aircraft which cannot fly at minimum operational weight for flight control reasons and must have some ballast added if there is no cargo.

In many cases, minimum weight is unreachable in any sort of normal configurations.

The question is concerning the definition of specific terminology, this is not a slang or lay-speak use of minimum weight. The minimum weight in question is inherently reachable by the definition of the parameters.

So it's not a limitation?  But see "On the A310 freighter there is a 'Minimum Flight Weight' ie the take-off weight of the aircraft must be at or above this weight to depart.". From https://aviation.stackexchange.com/a/66487/34686  .

The Bombardier CRJ 700 is a has two rear jet engines with a T tail and a long forward fuselage.  It's MTOW is around 75,000 lbs, allowing for around 33,000 lb combinations of passengers, cargo, and fuel. The 42,000 lb "minimum weight"  (also listed as 44,000 lbs) would be a useful tool to determine safe loading of the aircraft.
But one other criteria for loading is Center of Gravity.  Many CG diagrams look like a lopsided rectangle, especially for the utility category.  Heavier loads favor more rearward placement.  It occurred to me that some aircraft actually require a brace to keep the tail from dropping when completely unloaded.
So, "minimum weight" (for safe flying) may be different from "empty weight" because empty CG is too far aft. Further reading into the CRJ 700 POH with attention to CG charts may be in order.


text:
What are the criteria for "variable" in METAR reports?
Regarding variable wind direction in METAR reports, what are the criteria for VARIABLE when the authority uses "VRB"?
An Advisory Circular mentions the authority uses "V" when the wind direction varies by 60 degrees. But how about "VRB"?

Variable less than 60° and less than 6 knots. If you don't get an answer by the morning I'll find the official source.

Thank you for the reply. As long as I read AC, I couldn't find the answer.

There are two official sources to take into account:

ICAO Annex 3 to the Chicago Convention is the reference for meteorological information. Annex 3 applies to all ICAO members (countries), unless stated otherwise.

Members departing from ICAO recommendations state differences in their country AIP, section GEN 1.7.

ICAO Annex 3
§ 4.1.5.2:

when the total variation is 60° or more and less than 180° and the
wind speed is 6 km/h (3 kt) or more, such directional variations shall
be reported as the two extreme directions between which the surface
wind has varied

when the total variation is 60° or more and less than 180°
and the wind speed is less than 6 km/h (3 kt), the wind direction
shall be reported as variable with no mean wind direction; or

when the total variation is 180° or more, the wind direction shall be
reported as variable with no mean wind direction"

So for ICAO there are three cases:

The wind is significant (more than 6 km/h) and there is a predominant direction (varying by less than 60°), possibly with some gusts: the three data are reported in the form 31015G27KT.

There is a significant wind (more than 6 km/h) but the direction varies a lot (between 60° and 180°): Mean direction, speed and gust are reported in the same form, and direction range is reported using V, e.g. 31015G27KT 280V350.

There is no clear wind direction, either because the speed is low (less than 6 km/h) or the direction varies by more than 180°: No direction is reported, only a speed with the indication VRB is used, e.g. VRB02KT.

Country AIP
US AIP:

The wind direction may be considered variable if, during the 2-min
evaluation period, the wind speed is 6 KT or less. Also, the wind
direction shall be considered variable if, during the 2-min evaluation
period, it varies by 60 deg or more when the wind speed is greater
than 6 KT.
Practices define wind gusts as rapid fluctuations in wind
speed with a variation of 10 knots or more between peaks and lulls.
Wind speed data for the most recent 10 minutes is examined and a gust,
the maximum instantaneous wind speed during that 10-minute period, is
reported if the definition above is met during that period.

ATC instructions given in PANS ATM Doc 4444, § 12.3.1.7a are also refined:

In the U.S., the criterion for a variable wind is: wind speed greater
than 6 kt and direction varies by 60 degrees or more. If the wind is >1
kt but <6 kt, the wind direction may be replaced by ”VRB” followed by
the speed or reported as observed. “VRB” would be spoken as “wind
variable at .”

In the US, VRB indication is slightly different than in ICAO recommendations: VRB can be used regardless of the direction variation, when the wind is less than 6 kt (not 6 km/h) or if the variation is more than 60°. This covers the last two cases of ICAO.

METAR panel at Weeze tower (EDLV). source: Airplane Pictures, photo by Zonan Adolfse

The link to annex 3 doesn't seem to work anymore. Here is a new link to the 2010 PDF on the ICAO website: https://www.icao.int/airnavigation/IMP/Documents/Annex%203%20-%2075.pdf . The latest version seems to be behind a paywall, though

@Ulu83: Thanks, fixed. In case you need other annexes or documents, the site of the Swiss Federal Office of Civil Aviation is reliable (and yes, not the latest versions).

Thanks to mins, I could find out the answer for USA.
US AIP Section GEN 1.7 mentions below;

In the U.S., the criterion for a variable wind is: wind speed greater than 6 kt and direction varies by
  60 degrees or more. If the wind is >1 kt but <6 kt, the wind direction may be replaced by ”VRB”
  followed by the speed or reported as observed. “VRB” would be spoken as “wind variable at
  .”

The conclusion is VRB is used when variable less than 60° and less than 6 kt.

This doesn't seem to add anything to the existing answer. Please accept the other answer instead of repeating it as another anwser. This is a Q&A site, not a forum